1. Field of the Invention
The present invention relates to an electrostatic spray apparatus for applying a liquid coating material to a work piece, and more particularly to such apparatus which comprises a rotating, bell-like or disc-like atomizer head, the coating material being applied to its inner surface and being catapulted from its edge, and comprising an annular gap which is coaxial with the atomized head and connected to a compressed air source which ejects a compressed air jacket surrounding the atomized coating material.
2. Description of the Prior Art
Conventionally, the additional use of compressed air is considered as not being required in electrostatic rotary atomizers because the electrostatic field existing between the rotary atomizer and the work piece deflects the paint catapulted from the atomizer by a centrifugal force and atomized to the work piece and transports it to the work piece. The elimination of an additional compressed air flow, for example, in the direction towards the work piece, however, presumes that the centrifugal force imparted to the paint particles is relatively slight, i.e. the atomizer head is driven at a low speed. The latter, however, involves the disadvantage that the paint throughput, i.e. the amount of paint catapulted and sprayed per time unit is small. Higher and higher rotational speeds of the atomizer head have therefore been employed to increase the paint throughput.
In order to prevent a considerable portion of the paint particles from erupting out of the electrical field as a result of the great influence of the centrifugal force, it is known in the art to provide an annular gap which is coaxial with the atomizer head and which is connected to a compressed air source which produces a compressed air jacket surrounding the atomized coating material (paint cloud). It is further known to also employ the compressed air jacket to match the size or, respectively, diameter of the paint cloud to the respective requirements. It has been demonstrated in practice, however, that certain difficulties occur despite the air jacket. Therefore, particularly given very high atomizer head rotational speeds, an air pressure of considerable magnitude must be selected in order to therefore prevent an eruption of paint particles and an undesired increase in the diameter of the paint cloud. Air streams having such high pressure, however, lead to undesired turbulences and lend the paint particles such high kinetic energy that the influence of the electrostatic field (paint encompassing the work piece) is at least partially canceled. It has further turned out that an air jacket emitted by an annular gap is not sufficiently capable of doing justice both to the requirements of adjustability in the size of the paint cloud and the requirements of avoiding an eruption of paint particles, and as low as possible a flight speed of the paint particles in the direction towards the work piece.